High-Latitude, Shallow Marine Sedimentation during the Late Paleozoic Gondwanan Ice Age: The Early Permian Wasp Head Formation, Sydney Basin, Australia

Michael C. Rygel¹, Christopher R. Fielding¹, Kerrie Bann², Tracy Frank¹, and Lauren Birgenheier^1
1 University of Nebraska-Lincoln, Lincoln, NE
² Ichnofacies Pty. Ltd, Calgary, AB

The early Permian (early to middle Sakmarian) Wasp Head Formation is a shallow marine unit deposited at ~60° S latitude on the Panthalassan margin of Gondwana. This unit records a period of cold, glacially-influenced deposition between two more pronounced glacial periods (late Asselian-earliest Sakmarian and late Sakmarian).

The basal Wasp Head Formation contains up to four sedimentary breccia bodies separated by trough, and hummocky cross-stratified sandstone with interbedded conglomeratic lenses, abundant outsized clasts and locally common Skolithos and Cruziana Ichnofacies elements. These characteristics suggest deposition in a middle to upper shoreface with a coarse-grained contribution from ice-rafted debris (conglomerate and outsized clasts) and debris flow deposits derived from the basin margins (breccias). The upper part of the formation consists of four stacked successions of heavily-bioturbated (Cruziana Ichnofacies), muddy sandstone with conglomeratic lenses and outsized clasts that pass upwards into hummocky cross-stratified sandstone (Cruziana to Skolithos Ichnofacies). Within these successions, the transition from muddy, clast-rich intervals to sandy, clast-poor intervals are interpreted as fluctuations between offshore and shoreface environments. Heterolithic lithologies with a complex suite of sedimentary structures and stressed trace fossil suites suggest a strong deltaic influence locally. A transgressive surface of erosion and Glossifungites Ichnofacies marks the transition to the interbedded mudrocks and diamictites of the lower Pebbley Beach Formation – a unit deposited in association with the late Sakmarian glacial event.

Recent studies of this and other high-latitude deposits in eastern Australia are providing new insight into the dynamics of one of the world's most important “icehouse” intervals.